The present invention relates generally to a single pass full color printing system and, more particularly, to a color printing system consisting generally of a raster output scanner (ROS) optical system and a quad-level xerographic unit and a penta-level xerographic unit in tandem which can print pixels producing black and white and all six primary colors without printing toner upon toner.
In the practice of conventional bi-level xerography, two charge levels are produced on a charge retentive surface such as a photoconductive member or photoreceptor. The highly charged (i.e. unexposed to a light beam) areas are developed with toner. The discharged (or exposed to the light beam) areas are not developed with toner. These two levels can be developed to print black and white.
In tri-level, highlight color imaging, unlike conventional xerography, upon exposure, three charge levels are produced on the charge-retentive surface. The highly charged (i.e. unexposed) areas are developed with toner, and the area most fully discharged is also developed, but with a toner of a different color. The intermediately charged (or partially discharged by a light beam) area is not developed with toner. Thus, the charge retentive surface contains three exposure levels; zero exposure, intermediate exposure, and full exposure, which correspond to three charge levels. These three levels can be developed to print, for example, black, white, and a single color.
In quad-level or four-level color imaging, upon exposure, four charge levels are produced on the charge-retentive surface. Thus, the charge retentive surface contains four exposure levels; zero exposure, a low intermediate exposure, a high intermediate exposure and full exposure, which correspond to the four charge levels. These four levels can be developed to print, for example, black, white, and two colors.
An illustrative example of a quad-level xerographic unit is found in U.S. Pat. Nos. 4,731,634 and 5,155,541, commonly assigned with this application and herein incorporated by reference.
A quad-level xerographic unit, unlike the bi-level and tri-level, does not produce color images that match the toner colors. Two of the toner colors are produced while the third color produced is a combination of one of those first two toner colors and a third toner color.
There are alternate quad-level xerographic units for carrying out the desired formation of three different color pixels on the photoreceptor means of the present invention. Some of these alternatives, such as U.S. Pat. No. 5,049,949, assigned to the same assignee as the present invention and herein incorporated by reference, do not use the combining of two color toners to form a third color pixel on the photoreceptor means, but rather directly deposit three different color toners upon the photoreceptor means without combination.
A single pass color printing system of a raster output scanner (ROS) optical system and two tri-level xerographic units in tandem will produce black and white and five of the six primary colors, with pixel next to pixel printing producing all but the strongest saturation of the sixth primary color, an additive primary color. However, only two of the three subtractive primary colors of cyan, magenta and yellow are available for toner dot upon toner dot to combine to produce the additive primary colors. This single pass color printing system is found in U.S. Pat. No. 5,223,906, commonly assigned with this application and herein incorporated by reference.
A full color process would print the six primary colors of cyan, yellow, magenta, blue, green, and red, in addition to black and white.
A single pass full color printing system of a raster output scanner (ROS) optical system and a quad-level xerographic unit and a tri-level xerographic unit in tandem will produce black and white and all six primary colors with toner upon toner. This single pass color printing system is found in U.S. Pat. No. 5,221,954, commonly assigned with this application and herein incorporated by reference.
Both of these prior art approaches require toner of one color upon toner of a second color and are referred to in the art as Dot-On-Dot (DOD). The additive primary colors of red, green and blue are formed by mixing the subtractive primary colors of cyan, yellow and magenta.
When the red, green and blue colors must be obtained by mixing the cyan, yellow and magenta colors, there is always some color deficiency in the red, green and blue. The red formed by DOD mixing of yellow and magenta cannot recreate the deep red tones observed in nature. Because of the limitations of magenta, the red from magenta and yellow is actually an orange-red and the blue from magenta and cyan has a purplish hue. Smaller but similar deficiencies exist in the cyan and can exist in the yellow.
The use of actual red, green and blue toners enhances the coverage of the color gamut and enables richer hues throughout in a full color printing system.
A penta-level xerographic unit produces five exposure levels on a photoreceptor. The five exposure levels select between a subtractive and an adjacent additive primary color in both the Charge Area Development (CAD) and Discharge Area Development (DAD). The exposure level intermediate between the CAD and the DAD results in white. The selection of two possible colors in CAD, or two possible colors in DAD, or the selection of no toner can be developed to print, for example, black, white, and three colors. This penta-level xerographic unit is found in patent application Ser. No. 08/422,203 filed contemporaneously, commonly assigned to the same assignee herein and herein incorporated by reference.
It is an object of this invention to provide a color printing system using a penta-level xerographic unit.
It is another object of this invention to provide a color printing system using a quad-level xerographic unit and a penta-level xerographic unit.
It is still another object of this invention to provide a full color printing system without toner upon toner.
It is yet another object of this invention to provide a full color printing system with the additive primary colors developed without combining subtractive primary color toners.
It is yet another object of this invention to provide a full color printing system by combining subtractive primary color toners utilizing toner-on-toner to produce the additive primary colors.